The proportion of females, in particular women of color, among veterans is increasing. This subset of veterans frequently develops lupus, a devastating systemic autoimmune disease. There is a need to understand the mechanism of lupus, and to train physician-scientists capable of managing this disease using innovative approaches. Recent research findings have suggested that a class of T lymphocytes called regulatory T cells (Tregs) is centrally involved in regulating the immune system in health and disease, including in veterans. Current approaches to identifying Tregs in humans are poorly developed, as FoxP3, the marker of these cells in mice, is not as reliable in humans. Our studies suggest that a new marker, Helios, combined with FoxP3 allows for reliable identification of human Tregs. Helios-positive Tregs are validated as committed Tregs by use of gold standard tests showing that they do not make immune-activating cytokines and also have full demethylation of the FoxP3 gene, in contrast to Helios-negative FoxP3-positive cells, which make cytokines and are only partially FoxP3 gene demethylated. We demonstrate that in patients with more clinically severe systemic lupus erythematosus, there is a trend toward a lower ratio between Helios-positive Tregs and Helios- negative FoxP3-positive cells. In addition, we have found that Helios-positive Tregs increase in direct correlation with steroid therapy in lupus patients with low to moderate clinical severity. Moreover, we have observed that an inflammatory environment high in Type I interferon inhibits regulatory T cells. Based on these observations, we hypothesize that using Helios in combination with FoxP3 for identification of Tregs provides a more reliable method to evaluate immune disturbance and response to therapy. We also hypothesize that Type I interferon suppresses Treg expansion and activation, which is likely reversed by corticosteroids. In the proposed study, we will assess the validity of these hypotheses by addressing the following Specific Aims. In Specific Aim 1, we will validate Helios, in combination with FoxP3, as a definitive marker of natural regulatory T cells by expanding our study of Tregs in a larger number of patients with systemic lupus erythematosus. In Specific Aim 2, we will assert that Type I interferon drives expansion of effector T cells at the expense of regulatory T cells. We wil determine the mechanism by which Type I interferon inhibits regulatory T cells. In Specific Aim 3, cross-sectional analyses will be performed to determine how steroids may promote Treg expansion and possibly reverse the negative effects of Type I interferon. The goal of this research is to improve the well-being of veterans, particularly female veterans, by identifying those lupus patients who could benefit from therapy specifically aimed at stimulating Tregs. By investigating the mechanisms by which Type I interferon suppresses human Tregs and the pathways by which steroids promote human Tregs, we hope to discover new therapeutic targets in the treatment of not only lupus, but also a variety of autoimmune, allergic, and inflammatory disorders prevalent among veterans. Simultaneously, this work will allow the candidate to establish himself as an independent physician-scientist with a research focus in the regulation of the immune system in order to ultimately improve the lives of patients. The training and mentoring plans outline the path toward this goal by proposing a specific plan of coursework in translational research, biostatistics, and bioethics. The proposed research plan will expose the applicant to new research techniques in molecular biology and receptor signaling under the expertise of his primary mentor, Dr. Sergei Atamas. Dr. Violeta Rus, the first co-mentor, will provide clinical and research expertise in the care and study of patients with SLE. Dr. Marc Hochberg, the second co-mentor, will provide guidance in translational research and biostatistical methods. In addition, an advisory committee composed of renowned experts in T cell biology, FoxP3 epigenetics, clinical research, and training of junior investigators will help ensure that the applicant succeeds in becoming an independent physician-scientist serving veterans.